Which angles are at these selected edges?
The Angle information is going to be around the axis of the particular edge.  You can think about it as the angle between two adjacent faces.

In your example, the two 90 degree angles are formed between faces that are perpendicular to one another.  The 0 degree angle, however, is formed between two faces that exist in the same plane.

In other words, it's not measuring the angle between two edges.  For that, you would need to activate the Face Info Angle (shown in blue):



Edit: This might help visualize it a little more: